Advice please

I'm shortly going to do a round trip of 500 miles, mostly on motorways. I'm planning to start with the traction battery fully charged, and to re-charge on the motorway two or three times at the Ecotricity rapid charging outlets during toilet/tea breaks. On the motorway I'll set the car to 'eco' mode but hope fellow owners can advise, do I let the car do its own thing, or press the charge or save buttons, in order to maximise mpg, bearing in mind I may not be able to charge the battery at my destination before my return trip.

Your comments would be appreciated.

Eco mode will make a minimal difference if any. The most economical way to drive is to use "save" on the Motorway - and to use the electricity in slow traffic.

I make this kind of trip all the time (11K miles in just over 4 months) and don't even think about it. Would you ask this question if you drove a 'normal' car?

Just get in and drive, let the car do its thing.

If your destination is in an urban area, hit the Save button when the battery meter shows just under 50% after your last motorway charge, otherwise drive at SatNav accurate 70mph (where you can), get 35mpg and enjoy the comfort of the car.

Steel188 said:

If your destination is in an urban area, hit the Save button when the battery meter shows just under 50% after your last motorway charge, otherwise drive at SatNav accurate 70mph (where you can), get 35mpg and enjoy the comfort of the car.

Click to expand...

I totally agree with your response. Especially the 50% bit

Steel188 said:

Would you ask this question if you drove a 'normal' car?

Just get in and drive, let the car do its thing.

Click to expand...

Funny though, that you challenge the relevance of the question, yet choose the answer it :mrgreen:

The higher efficiency @ 50% is indisputable, but surely it is more effective to drive as much as possible on electricity at lower speeds to arrive at the chargepoint empty. Thus a higher level of charge on the motorway may well turn out to be the better option.

Although steverally says the charge points are on the motorway, I would agree. But then it would still be better / more efficient to let the SOC drop freely and regain the needed SOC by means of the Charge mode towards the end of the high speed part of the trip.

You will notice that I said to hit Save at 50% only after the last charge before reaching his destination. This implies that one would arrive at previous charge points on empty.

As for driving at a slower speed to eek out the electricity, there are so many 50mph (80kph) speed controlled sections of motorway under repair, combined with our regular congestion, that getting a chance to cruise at 70 for many miles is a treat not to be missed.

The car is an 1800Kg brick, and the difference between 35mpg and 37, or 37 and 39mpg is so small that life really is too short to worry about it. As I said before, don't think about it; get in, drive and enjoy it..

anko said:

Although steverally says the charge points are on the motorway, I would agree. But then it would still be better / more efficient to let the SOC drop freely and regain the needed SOC by means of the Charge mode towards the end of the high speed part of the trip.

Click to expand...

Which will (just) work @ 70 MpH, but not @ 130 KpH.

Thank you all for your responses.

anko said:

Although steverally says the charge points are on the motorway, I would agree. But then it would still be better / more efficient to let the SOC drop freely and regain the needed SOC by means of the Charge mode towards the end of the high speed part of the trip.

Click to expand...

However, it is also useful to have some battery "in reserve" because not only are some Services quite a long way from the motorway itself e.g. Dartford Tunnel but you never know when you are going to be stuck in slow moving jams where you don't want to be breathing in your own traffic fumes

greendwarf said:

anko said:

Although steverally says the charge points are on the motorway, I would agree. But then it would still be better / more efficient to let the SOC drop freely and regain the needed SOC by means of the Charge mode towards the end of the high speed part of the trip.

Click to expand...

However, it is also useful to have some battery "in reserve" because not only are some Services quite a long way from the motorway itself e.g. Dartford Tunnel but you never know when you are going to be stuck in slow moving jams where you don't want to be breathing in your own traffic fumes

Click to expand...

Totally makes sense. Bottom line would be: Feel free to save some battery charge for special occasions. But do not hit Save as soon as you enter the motorway, but only after you are down to less than 50% SOC (on the dash).

Unless you know that you will need a full charge further on...

jaapv said:

Unless you know that you will need a full charge further on...

Click to expand...

When do you need a full charge, if I may ask?

Mountains ahead, or 30/40 Km of urban traffic after leaving the motorway, a few hours of congestion, etc.

Anko, why do you say that 'Save' should not be used until the SOC is below 50%.

Graham

When you look at a PHEV as a hybrid vehicle and forget about the plug-in bit for a while, its efficiency is based upon the fact that the battery serves as a buffer: when the engine runs, it not only drives the car but also recharges the battery. Therefor it is put at a higher load and thus runs more efficiently. As a payback,the engine can be turned off every now and then. The faster the battery recharges, the higher the load / efficiency and the more often the engine will be switched of (%-age wise).

When SOC goes up, the battery accepts less incoming power/ recharges slower. The engine runs at a lower load and thus less efficient, plus it runs more often. I have seen the first reduction of battery recharge current at 50% (65% real). At even higher %-ages, this effect increases.

Also we know that the regen effect is less at a higher SOC. Less regen means more use of friction brakes. But I think for this, you need to be way higher than 50%.

Thanks Anko for the clear explanation.

Something I've mentioned earlier:

In parallel hybrid mode with CC engaged, the car can maintain the set speed by simply playing with the charge current. Engine load does not fluctuate. But with SOC > 50% the charge current is restricted and the car will need to play with the throttle to maintain speed. Less effective and (IMHO) less efficient as well,

That's finally an explanation of an observed phenomena: when driving at the limit of its capability (charge on), the battery level will drop fairly rapidly and stabilize around 40%.

jaapv said:

That's finally an explanation of an observed phenomena: when driving at the limit of its capability (charge on), the battery level will drop fairly rapidly and stabilize around 40%.

Click to expand...

Under such conditions, you loose SOC while driving at constant speed and especially while accelerating. How much you loose is not affected by SOC (until you get towards 20% real SOC or so, which is not very likely). While coasting and especially during regenerative braking, you will gain some. How much you gain is affected by SOC. So yes, why not. Only I cannot relate to the 40%, as I have never seen a step down in charge current when SOC reached 40%. Of course, I could have missed it ....